In this project we have focused on characterizing biochemically, genetically, and developmentally the isozymes of L-glycerol 3-phosphate dehydrogenase (EC 1.1.1.8) in the mouse. The isozymes are differentially expressed during development in vivo and in tissue culture. A common denominator of the conditions required for transition from embryonic to adult isozyme expression is that cell contact must be maximized. This project intends to focus on further exploring the nature of this apparent cell-contact mediated regulation of a specific genetic locus. The experiments include measuring the amount of specific messenger RNA for adult L-glycerol 3-phosphate dehydrogenase in cells in culture during the period of increased enzyme synthesis, and manipulating cell-to-cell contact of reaggregating mouse cerebellar in an attempt to identify cell surface components involved in gene activation.